Elastomeric compositon comprising a benzene-soluble chloroprene polymer and a benzene-insoluble radiation cross-linked chloroprene polymer



United StatesPatent O ELASTOMERIC COMPOSITION COMPRISlNG BENZENE-SOLUBLE CHLOROPRENE POLYMER AND A BENZENE-INSOLUBLE RADIATION CROSS-LINKED CHLOROPRENE POLYlVLER Rudolph Pariser, Brandywine Hundred, and Robert D.

Souflie, Mill Creek Hundred, Del., assignors to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed July 31, 1959, Ser. No. 830,734

, 7 Claims. (Cl. 260-455) This invention relates to novel elastomers and more particularly to easily processable elastomers comprising blends of chloroprene polymers.

It has long been known that chloroprene polymer elastomers may be increased in plasticity by being prepared in the presence of so-called modifying agents or by being treated, after their formation, with plasticizing agents. The control of plasticity, however, is not the whole answer to the problem of producing an elastomer which has good working properties, that is, is capable not only of being easily formed into the desired shape by passage between the rolls of a rubber mill or by extrusion through a die, but also of retaining its shape, size, and smooth surface after the force by which it has been molded is removed. Elastomers in general do not completely retain the exact size and shape into which they are formed by a rubber-working machinery; This characteristic, known as nerve or elastic memory, is present in chloroprene polymers to a greater extent than in'natural rubber and somewhat interferes with its use in certain delicate operations such as the high-speed extrusion of complicated shapes.

It is an object of the present invention to provide an elastomer which may be easily processed. A further object is to provide an elastomer comprising ablend of chloroprene polymers, which elastomer has greatly improved working properties. A further object is to pro vide a process for the preparation of an improved elastomer comprising a blend of chloroprene polymers. Other objects will appear hereinafter.

These and other objects of this invention are accomplished by an easily processable elastomer comprising an intimate blend of (a) a plastic, benzene-soluble chloroprene polymer and (b) a cross-linked, benzene-insoluble chloroprene polymer obtained by exposing a chloroprene polymer in latex form to ionizing radiation producing the effect obtained by exposure to at least 3x10 rads of 0.5 to 5.0 mev. beta radiation at a dose rate of about 10 to 10' rads per second, the ratio of (a) to (b) on a weight basis being between about 1:4 and about 4:1. One rad is the quantity of radiation which will result in an energy absorption of I ergs per gram of irradiated material.

The novel easily processable elastomer of the present invention is obtained by blending a plastic, .benzenesoluble chloroprene polymer with a cross-linked benzeneinsoluble chloroprene polymer which has been exposed to a prescribed amount of ionizing radiation. In other words, the elastomer is a blend of irradiated and unirradiated chloroprene polymers.

The plastic, benzene-soluble chloroprene polymer component of the elastomer is a polymer obtained by the polymerization of chloroprene, i.e., 2-chloro1,3-butadiene. These chloroprene polymers are described in US. Patents 1,950,436; 2,227,517; 2,234,215; 2,371,719; 2,- 463,225 and 2,481,044.

The preferred chloroprene polymer is obtained by partial polymerization of chloroprene in the presence of-an aliphatic mercaptan such as dodecyl mercaptan. It is to g be understood that the term chloroprene polymers, as

urated monomers such as styrene, acrylic nitrile, methyl methacrylate, butadiene and 2,3-dichlorobutadiene-L3.

The irradiated or cross-linked benzene-insoluble chloroprene polymer may be any of the chloroprene polymers described above which have been subjected to ionizing radiation. Prior to radiation these chloroprene polymers may originally be plastic or non-plastic but when they are subjected to ionizing radiation they should be in the form of an emulsion or latex. The solids content of the latex is not critical and may range from about 20 to 60%. The manner in which these chloroprene polymers are subjected to ionizing radiation as well as the amount of such radiation will be more fully discussed hereinafter.

The proportion of irradiated chloroprene polymer in the blend of the present invention may range from about 20 to about 80% by weight. As the amount of irradiated chloroprene polymerin the blend increases, the working properties of the elastomer, as shown by the nerve number, tend to improve andultimately pass through a max- When the blend contains more than about 80% of irradiated chloroprenepolymer the working properties of the elastomer tend to be unsatisfactory. I At the lower 1 end of the range, i.e. around 20%, the tensile properties of the elastomer tend tolbe improved. The preferred amount of irradiated chloroprene polymerin the total blend is fromabout to Thepreferred weight ratio of irradiated to plastic polymer in the blend is between 9:11 and 1li9. 1

In addition to the two components in the .novel elastomer of the present invention, i.,e. the plastic, soluble chloroprene polymer and the cross-linked, insoluble chloroprene polymer, 2. third component may be present if desired. This third'component is a fluid chloroprene greater than 0.1.. When using. the fluid chloroprene polymer as a third component, the resulting elastomer after extrusion tends .to have a smooth surface.

As mentioned above, one of the. components of the blend is a cross-linked, benzene-insoluble chloroprene polymer which is obtained by. exposing a chloroprene polymer inlatex form to ionizing radiation. Suitable ionizing radiation includes bothradiation in the form, sometimes regarded as particle radiation andradiation in the form sometimes regarded as ionizing electromagnetic'radiation. By particle radiation is meant astream of particles such as electrons, protons, neutrons, alpha particles, deuterons, beta-particles, or thelike, so "directed that A the said particle impinges upon the chloroprene polymer in latex form. The charged particles may be accelerated bymeans of a suitable voltage gradient, using such devices as a cathode ray tube, resonant cavity accelerator, a Van de Graafi accelerator, a Cockcroft-Walton accelerator, orzthe like, as is well ,knownto those skilled in the art. Neutron radiation may be produced bysuitable nuclear reactions, e.g., bombardment of a beryllium target with deuterons or alpha-particles. In addition, particle radiation maybe obtained from an atomic pile,

By ionizing electromagnetic radiation is meant radiation of the type produced when a metal target (e.g., gold 4 fairly high loading of clay is used'as is customary in making tubing and other extruded articles, but the elastomers may also be used to advantage in gum stocks and stocks reinforced with carbon black. Waxes, oils and other or tungsten) is bombarded by electrons possessing appro- 5 softeners and lubricants should in general be used but priate energy. Such radiation is conventionally termed large amounts are not necessary. The optional fluid X-ray.' In addition to X-rays produced as indicated above, chloroprene polymer in the blends maybe replaced partly ionizing electromagnetic radiation may be used and may or wholly by various oils and softeners without much he obtained from a nuclear reactor (pile) or from 7 change in processing characteristics but with some loss natural or artificial radioactive material. In all of these 10 of tensile properties. -latter cases the radiation is conventionally termed gamma The novel elastomers of the present invention which rays. p are made up of a blend of two different chloroprene poly- It is recognized that the energy characteristics of one mers and, if desired, a third component which is a fluid form of :ionizing radiation can be expressed in terms chloroprene polymer, display greatly improved working which are appropriate for another form. Thus, it is acproperties. Although the greatly improved working ceptable to refer to energy equivalents between, for examproperties of the elastomers of this invention are described ple, radiation commonly considered asparticle radiation in the following examples largely in terms of extrusion and radiation commonly considered as wave or electrostocks, their properties alsomake them valuable in fi'icmagnetic radiation. The eifect of the ionizing radiation tion and calender stocks. These elastomers may be emupon a chloroprene polymer, altering it in such a way ployed for the same purposes as the plastic chloroprene that it gives blends of improved processing properties, polymer elastomers which are now produced commercialdepends on the type of radiation, the dosage (energy ly. Thus,--they may be processed in any formof rubbera'bsorbed per weight unit of chloroprene polymer) and working equipment, such as internal mixers, compounding .the dose rate (dosage per unit of time), withthe latter mills, calenders, e'xtruders and the like, in fabricating two varyingover very wide ranges. At present, the relatires and mechanical goods of all kinds, coated fabrics, tion of these variables is not fully explored. Ineach tubing',c'oated wire,a'nd extruded gaskets. The elastomers case, however, there is areadily determined are particularly valuable where it is important to have a dosage, dependent upon the dose rate and type of radismooth surface and minimum shrinkage.

ation, which will produce the effect upon the chloroprene ,The following examples will better illustrate the nature polymer required by the present invention. For beta of the present invention; however, the invention is not radiation at a dose rate of about 10 to 10" rads per intended to belimite'd to these examples. Parts are by second, this minimum dose is about 3X10 rads. For 7 weight unless otherwise indicated; '3 mevl gamma radiation at a dose rate of 12.5 10.1250 7 a rads per second, this minimum is about 1.5 I0 rads. 1 V A particle energy of 0.5 to 5.0 mev. is usually preferred. (A) 'A polyehloroprene latex made by polymerizing The amount of ionizing radiation usedto cross-link chloroprene dispersed in a sodium rosinate solution in the chloropr'ene polymerin the latex form is critical. the presence of about 0.25 percent-of dodecyl mercaptan Thus, itis notenough merely to irradiate since a wide so as to give 'a plastic product when isolated directly, is range of lower amounts of radiation produces a cross- 7 used as the starting material. In making this latex, polylinked 'chloroprene polymer which in the blend results merization is carried to about70 percent of completion in an elastomer which does not show the desiredimproveat 40 C. and the unchanged .chloroprene is removed by *ment in working properties.- As mentioned above, the V distillation. This latex contains about 38 percent of polyj chloroprene polymer in latexform should be subjected chloroprene. to a dose equivalent to. at least 3 X 10 rads of 0.5 to 5.0 r (B) Part of the latex prepared in A above is irradiated mev. beta particle radiation at a dose'rate of aboutlO with 2 mev. beta radiation from a Van de Graaff electrotol0" rads per second. When the irradiation is above static generator operated at a beam current of 250 microabout this figure, the working properties of the blends amperes corresponding to a power output of 500 watts. are better than those of the chloroprene polymer plastic The latex (one liter at a time) iscontained in a pan meas- 7 component per se and the working properties are improved uring' 8 by 24 inches and made of stainless steel, covered :further with further increase of irradiation. It has been with a film of polyethylene terephthalate 0.0075 inch determined that at the higher irradiation levels there is thick, in a nitrogen atmosphere. This pan is moved on 1 a definite-but not serious decrease of tensile properties a grounded aluminum table 1 0 cms. below the aluminum of the elastomer. By varying'the amount of irradiation exit window of the generator at such a rate that it is of fi Q P lPQ Y eglastomfir exposed to the radiation for 1.1 second per pass. The y'b obtzfmed of essenflally ha g Propeftles power per square centimeter of latex surface'is approximuch i m g m PF D elasfomer mately 10 watts and the absorption is 11 watt-seconds per Y' b i g PmPemes 'Wlth pass. corresponds to 11x10 rads per pass. The i vyqrkmg mP general the'qllam layer of latex is approximately 1 cm. thick and the radiatityof irradiatlonqshould notexceed theefiect obtained ti bsf Tabs) b that Afte :by exposure to about 25.Xl,0 rads of0.5 to 5.0 mev. beta 9 1 5 Pi r radiation at a dose rate of a out 10 to 107 rads per second. 1 i or g (ati Z i i i a quan' Afiefthe chloropreneppolymer 7m latexrform has been my of a short-stop dlSPBl'SlOIl containing 0.03: percent, irradiated to formca cross-linked insolublechloroprene 9n therwglght of hem??? i tafrtlary'butyl polymer, the mad'iated and d a Plastic soluble catechol and 0.03 percent phenothiazme is added to pre- Y'chloroprene]polymer may be blended by mixing the two Vent a y u er ter tion- The latex 1s then ready for 5g pa 'g tg a l ti es andih'n' mfing m n by blendingwith other latices, as. m some of the following conventional meanssuch as coagulation byfreezing. It examplesis also possible to blend the two components as solids, In' the present example the irradiated polymer is isoeven though one of themis'non-plastic, by mechanical lated' by adjusting the pH to 5.6-with acetic acid and means, for example or lay-working in an internal coagulating-by freezing'in a thin layer on a rotating drum mixen such as a Banbury or Werner-Pfleiderer The compoundingof the elastomers of the present inventionis like thatof the 'pla'sticchloroprene polymers, as described in The-Neoprenes published in 1953 by 1. du Pont de'Neni'ours and- Co. In the examples, a

at -l5 (3., removing the polymer as a continuous sheet,

washing with water at 45 (3., and drying. The polymer is then ready for dry blending with the other ingredients.

(C) A fluid polychloroprene latex is made by polymerizing in a sodium r'osinate solution in the presence of d percent of dodecyl mercaptan at 40, coagulating with acid and isolating and drying the fiuid product.

(D) A blend is now made from 45 parts of the irradiated polymer prepared in B above, 5 parts of the fluid polymer prepared in C above, and 50 parts of an unirradiated plastic polymer which has been isolated directly from the latex prepared in A above. The blending of the dry components is carried out in an internal mixer during the compounding step. The non-plastic, irradiated polymer is rapidly dispersed with the compounding ingredients giving a plastic, easily worked mass. The clay stock used to evaluate the product has the following composition:

Parts Polymer blend 100 Phenyl alphanaphthylamine 1 Magnesium oxide 4 Zinc oxide 5 Clay 90 Lubricating oil 12 Parafiin wax l Petrolatum 1 Z-Mercaptoimidazoline 0.5

The resulting stock shows very good working properties and cures readily at 307 F. for 30 minutes to a vulcanizate having excellent physical characteristics. A comparison is also made with the plastic, unirradiated component of the blend alone and with a commercial chloroprene polymer of excellent processing characteristics, madeby another method. The properties of these are:

The above stocks are also compared after extrusion through a two inch Royle extruder operating at 35 r.-p.m. fitted with a Garvey die, at 205 F. The stock from the blend of this example gives a very smooth extrudate with a continuous feather edge. The die swell, i.e., the weight in grams of one inch of extrudate is 1.86, which is very low. In all these respects the stock is at least as good as the commercial polychloroprene designed for excellent processing and is much superior to the plastic unirradiated polychloroprene which has a die swell of 2.29 and gives a rough extrudate with a broken feather edge. Note also that the tensile properties of the blend of this example are as good as those of the plastic polychloroprene polymer.

In quantitatively evaluating the working properties of the elastomers of this invention, an unoflicial test has been used, which give a quantity called the nerve number. A SO-grarn sample of the elastomer to be tested is milled for 6 minutes at 50 C. on a laboratory rubber mill with rolls 2 by 6 inches, and is then sheeted olf with the mill clearance set at 25 mils. The sheet is allowed to stand 20 minutes at room temperature. Strips 1 by 2 inches are then cut out and weighed. The average final thickness of the strips, which have thickened to a greater or less extent depending on the nerve of the material, is calculated fiom the weight, area, and density of the strip. The nerve number is the ratio of the final to the original thickness, minus 1. The nerve number is determined prior to curing.

In all of the following examples, the elastomers are compounded with the same formula as listed in Part D of this example and all the stocks are cured at 307 F. for 30 minutes.

Example 2 Example 1 is repeated with the exception that the plastic, unirradiated chloroprene polymer is a copolymer which contains about 3 percent of 2,3-dichloro'butadiene- 1,3. The irradiated polymer and the fluid latex are the same as used in Example 1. The properties of the blended polymer and that of the plastic unirradiated polymer are as follows:

Blend of this Example Plastic chloroprene polymer alone Nerve No Tensile strength at break, lbs./

sq. in Elongation at break, 25C., percent Modulus at 300% elongation, 25C., 1bs./

Example 3 This example is identical with Example 1 except that the polymer to be irradiated is made without mercaptan and is therefore non-plastic and that all three components are blended in the form of the latices in which they are made and the material is isolated from blended latex by freezing as described in Example 1 (B). The irradiated polymer, plastic polymer and fluid polymer are in the ratio of 49:46 :5. This latex blending procedure is used in all the following examples. The elastomer has the following excellent processing properties:

Nerve No. 1.5 Tensile strength at break, 25 C., lbs/sq. in. 1,815 Elongation at break, 25 C., percent 620 Modulus at 300% elongation, 25 C., lbs/sq. in. 735

Example 4 Thisis not an embodiment of the invention, since the amount of irradiation to obtain the cross-linked, insoluble polychloroprene is only 2 passes, or 2.2)(10 rads. The irradiated polymer, plastic polymer and fluid polymer are in the ratio 50:45 :5 and are blended as latices, the ex- Nerve No. 2.6 Tensile strength at break, 25 C., lbs/sq. in. 2,100 Elongation at break, 25 C., percent 710 Modulus at 300% elongation, 25 C., lbs/sq. in. 888

Examples 6 and 7 These are identical with Example 5 except for higher irradiation (5 and 10 passes, respectively) and a very minor change in polymer ratio to 47:48z5. The properties are as follows:

7 i Example 8 This is identical with Examples through 7 excep for a' still higher irradiation passes) and another very minor shift in ratio to 48:47:5. The properties are as Exampl 9 This is identical with Example 8 except that there is no fluid polymer in the blend, the ratio of irradiated to unirradia-ted polymer being 50:50. The tensile properties are improved by this omission but extrudates lack the extreme smoothness of Example 8. The properties are as follows:

NerveNo. Tensile strength at break, C., lbs/sq. in 1,875 Elongation at break, 25C., percent 500 Modulus at 300% elongation, 25 f C., lbs/sq. in. 1,067

' Example 10 This is identical with Example 9 except that the ratio of irradiated to unirradiated polymer is 25:75. The prop erties are as follows: 1

I Q Q V Tensile strength at break, 25 C., lbs/sq. in. 2,160 Elongation at break, 25 C., percent 670 Modulus at 300% elongation, 25 (3., lbs./ sq. in. 848

' Example 11 This is identical with Example 6 except that the ratio of irradiated, plastic and fluid polymers 75 :2015. The properties are as follows:

Nerve No. 1.3 Tensile strength at break,,25 C., lbs/sq. 1,825 Elongation at break, 25 0., percent 670 Modulus at 300% elongation, 25 C., lbs/sq. in. 748

Example 12 1.8 X10 rads. The properties are as follows: NerveNo. 1 V ,v 7 1.9 Tensile strength at break, 25 C., lbs/sq. in. 2,225 Elongation at break, 25 C., percent 800 Modu M 7 e o at 2 3-. q- 5 As. ma y w dely d f er n emb m ts o th s i e tion may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as-defined in the appended claims.

We claim:

1. An easily processable elastomer comprising an intimate blend of (a) a plastic, benzene-soluble chloroprene polymer and (b) a cross-linked, benzene-insoluble chloroprene polymer obtained by exposing a chloroprene polymer in latex form to ionizing radiation producing the efiect obtained by exposure to at least 3 X 10 rads of 0.5 to 5.0 mev. beta radiation ata dose rate of about 10 V to 10" rads per second, the ratio of (a) to (b) on a Weight basis being between about 1:4 and about 4:1, said chloroprene polymers being selected from the group consisting of polychloroprene "and copolymers ofchloroprene with up to about 10 percent by' weight of another polymerizable ethylenically unsaturated monomer.

2. An elastomer according to claim 1 wherein the ionizing radiation is in the form of 2.0 mev. beta radiation at a dose rate of about 10 rads per second.

3. An elastomer according to claim 1 wherein the ionizing radiation is in the form of 3 mev. gamma radiation at a dose rate of 12.5 to 1250 rads per second for a dose of at least 1.5)(10 rads.

4. An easily processable elastomer consisting essentially of an intimate blend of (a) a plastic, benzenesoluble chloroprene polymer, (b) a cross-linked, benzene-insoluble chloroprene polymer obtained by exposing a chloroprene polymer in latex form to ionizing radiation producing the effect obtained by exposure to at least 3X10 rads of 0.5 to 5.0 mev. beta radiation at a dose rate of about 10 to 10" rads per second, and (c) a fluid chloroprene polymer prepared by polymerizing chloroprene in the presence of enough mercaptan so that the resulting chloroprene polymer has an intrinsic viscosity in benzene of not greater than 0.1; the ratio of (a) to til (b) on a weight basis being between about 1:4 and 4:1, the amount of (a) and (b) comprising at least about percent by weight of the blend and the amount of (c) comprising no more than about 20' percent by weight of the blend, said chloroprene polymers being selected from the group consisting of polychloroprene and copolymers of chloroprene withup to about 10 percent by weight of another polymerizable ethylenically unsaturated monomer.

5. An elastomer according to claim 4 wherein the ionizing radiation is in the form of 2.0 mev. beta radiation at a dose rate of about 10 ,1'ads per second.

6. An elastomer according to claim 4 wherein the ionizing radiation is in the form of 3 mev. gamma radiation at a dose rate of 12.5 to 1250 rads per second for a dose of at least 1.5x l0 rads.

7. An elastomer according to claim 4 wherein the weight ratio of plastic chloroprene polymer to irradiated chloroprene polymer is between about 9:11 and 11:9.

No references cited. 

1. AN EASILY PROCESSABLE ELASTOMER COMPRISING AN INTIMATE BLEND OF (A) A PLASTIC, BENZENE-SOLUBLE CHLOROPRENE POLYMER AND (B) A CROSS-LINKED, BENZENE-INSOLUBLE CHLOROPRENE POLYMER OBTAINED BY EXPOSING A CHLOROPRENE POLYMER IN LATEX FORM TO IONIZING RADIATION PRODUCING THE EFFECT OBTAINED BY EXPOSURE TO AT LEAST 3X106 RADS OF 0.5 TO 5.0 MEV. BETA RADIATION AT A DOSE RATE OF ABOUT 105 TO 107 RADS PER SECOND, THE RATIO OF (A) TO (B) ON A WEIGHT BASIS BEING BETWEEN ABOUT 1:4 AND ABOUT 4:1, SAID CHLOROPRENE POLYMERS BEING SELECTED FROM THE GROUP CONSISTING OF POLYCHLOROPRENE AND COPOLYMERS OF CHLOROPRENE WITH UP TO ABOUT 10 PERCENT BY WEIGHT OF ANOTHER POLYMERIZABLE ETHYLENICALLY UNSATURATED MONOMER. 